Is there a way to have products or collection with a different tax group? For example, in my country VAT is 16%, however some commodities (e.g. milk) is excepted and is taxed at 4% only. Any way of doing that on WIX?
You can set this up with Avalara 
https://support.wix.com/en/article/creating-tax-groups-for-products-with-avalara-in-wix-stores